This invention relates in general to measurement systems and, in particular, to a self calibrating differential sensor for measuring pressure, chemical, electrical and other conditions.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a self calibrating differential sensor, such as for use in the measurement of pressure differential, temperature differential, differential chemical parameters and other physical parameters. The system of the invention is independent of base line or zero shift.
In the measurement of many conditions, the measuring device is subject to error due to shift of the base line of the calibration for the measurement. The introduction of such error may result from changes in numerous environmental or physical factors. This calibration problem is often encountered in pressure transducers in which a base line shift can occur in response to variations in temperature, barometric pressure, reference pressure, packaging stresses, deterioration of electronic components, and a variety of other causes. Such shifts are a major problem in fully implantable pressure transducers for living bodies where long-term biomedical applications are intended for five years or longer. Known devices require periodic calibration in order to maintain acceptable transducer accuracy, generally Emax=.+-.15 mm H.sub.2 O. This calibration procedure normally requires some type of invasive surgical procedure, such as, for example, lumbar puncture. It is generally accepted that base line shift is a major cause of transducer inaccuracy in body implantable applications.